circuit conflict , wrong transistor ?

hello.

Thanks to members on this forum, I have been able to build two little circuits and individually they work great, but I found that when I try and join them together they conflict.
in the picture attached, Circuit 1 takes a low voltage trigger signal and through use of the transistor it opens up the higher level 9v psu signal. Circuit 1 transistor opens and closes the connection of the - negative terminal, so with this circuit positive is always present on the main output. which causes a problem for circuit 2.

The second circuit is designed to light up a bulb when there is 'no' power present on the input; and then turns off the bulb when there 'is' power present on the input.

The problem is that whether the trigger circuit 1 is on or off ,it always has positive present at the terminals, so the second circuit responds to that and is always in the off position.

i wonder is there a way to have the trigger circuit 1 open and close positive instead of negative? Or perhaps circuit 2 could respond to the open and closing of the negative from circuit 1?

the diagram i made does not have regulators or relays as it just looked so messy. so i've simplified it a bit to aid explanation.

i hope someone can help.
thanks again : )

Circuit 1 looks wrong to me.

Where's circuit 1's output?

Going by the way it's drawn, all it does is connect the negative side of the battery to the 0V side of the 9V power supply which won't do anything.

How exactly are you connecting the two circuits together?

If all you want to do is turn an LED off when there's an input voltage, you can use one transistor but it's not very efficient.

Here's a circuit but as mentioned above, it's not very efficient because it actually uses more power when the LED is off. Another transistor can be added to improve the efficiency but it might not be important.

harps said:

hello.


i wonder is there a way to have the trigger circuit 1 open and close positive instead of negative?

i hope someone can help.
thanks again : )

Click to expand...

Here is one way for a pos. input to producew a pos. output.

Note: this is a simplified convention, actuality would need more components.

That's an emitter follower, the output is equal to the input minus the Vbe losses.

Thanks for the circuit but he needs it to work the other way round, he needs the output to be low, when the input is high.

hello : )

thanks again for your replies, i've altered the diagram a bit to help explanation.

i was hoping that a transistor would be more kind on the 9 volt psu than a perhaps a relay. ( i can make this work with relays but i thought a transistor would be more reliable and energy friendly as i am hoping to use lots of these circuits; and add relays where the leds are too (for audio). 8 or maybe 16 of these circuits from the one 9volt psu : ?

ive made both the circuits work( so thats good) but put them together and circuit two always goes off due to circuit 1's positive is always present at the output. ( circuit 1 gates the negative contact not the positive )

both circuits share the same 9 volt psu.

hope that makes sense. : P
thanks again for help.

If you want LED2 to be on all the time and then turn off when LED 1 comes on then this circuit will work for that.

It allows both circuits to interact with signal voltages only, using the same power supply, VCC.

The diode may or may not be needed depending on the signal strength needed for your aplication.
It is in there only as to give further isolation, from one circuit to the other.

If this is not what you want then please explain more about the circuit signals.
Such as The state of each circuit befor and during and after a input is recieved.
Then it can be taken from there with a new design, if needed.

Your schematic is a nightmare! I also wish it didn't have the chicken-pox dots all over it and the beige background.

1) In circuit #1, the base-emitter diode of the transistor will blow up without limiting the current from the +2V signal.
2) In circuit #1 the emitter of the transistor and the negative terminal of the +2V signal should connect to ground in the circuit #2.
3) The collector of the transistor in circuit #1 should connect to the input of circuit #2.
4) The LED and current limiting resistor in circuit #2 should connect in series with the collector of the transistor and the positive supply.
I simplified and fixed your schematic.

You might want to increase the value of R1 otherwise LED 1 will glow dimly when LED 2 is on.

If it's increased to 10k, you will hardly be able to see D1 faintly glowing.

EDIT:
If you use a MOSFET for the second transistor (the 2N7000 should be fine) R1 can be increased to 1M which will will completlely eliminate the dim glow.

thanks JClrd , the circuit looks great, but after hours or experimenting i just could not make it work not sure if i used the right transistors (i have 2n2222 npn.)

thanks uncle scrooge i shall go and try yours now.

i found a new way to describe what i need now from looking at your diagram :

trigger signal on = LED 1 on & LED 2 off
trigger signal off = LED 1 off & LED 2 on

hope that makes more sense.

fingers cross i shall try again.

thanks everyone

hello. : )

i managed to make Uncle Scrooges circuit,

its very difficult to get a balance, instead of a 10k resistor i used a variable so i could tune it as best as possible.

below is the best i can get it to work : (i've rated the led brightness out of 10)

trigger signal on = LED 1= (9/10) brightness. LED2 = (3.5/10) brightness
trigger signal off = LED 1= (3/10)brightness. LED 2 =(dim 6/10) brightness


i found increasing the resistance ( between the two circuits) meant sacrificing the glow on the second led. As hero says perhaps a mosfet will help?
i'm hoping to power relays with this type of circuit too, the 2n2222 seems to take allot of juice from the 9v vcc supply I'm not sure this will work for relays too , unless the mosfet helps out. i shall buy one tomorrow and see.

i find:

circuit 1 is the easiest part to make and to use, i can get full glow on my 5v led : )
but the second circuit is very difficult and dim in brightness.

did someone mention a flip flop?

thanks.
: )

how about using solid state relays instead of transistors? anyone used one? are they efficient? perhaps they use less energy than a mechanical relay?

All right, you want it to suddenly turn on at a certain voltage so you need a Schmitt trigger.

Are you sure that's needed?

Does the input voltage vary between 0V and 2V or can it be either on or off?

harps said:

hello. : )

trigger signal on = LED 1= (9/10) brightness. LED2 = (3.5/10) brightness
trigger signal off = LED 1= (3/10)brightness. LED 2 =(dim 6/10) brightness




did someone mention a flip flop?

thanks.
: )

Click to expand...

TAKE CAREFUL NOTICE WHERE THE 2 OUTPUTS ARE LOCATED.

LEFT SIDE CIRCUIT HAS OUTPUT 2 AND THE RIGHT SIDE CIRCUIT HAS OUTPUT 1.

I did all this with my simulator and it has only 2v. 40mA. led's, so I strung 2 together for simulation purposes only.

This will have about 150 mA. draw.



This draws around 60 mA.

the trigger signal is dc 3.5 v

the VCC is actually 9.9 volts dc.

my leds are 5v
and the relays i hope to use in combination with the LEds are also 5v (40ma)

try the second one I just posted 2 posts up (#13) it should work.

thanks jclrd i shall try this tonight. : )

In my circuit, with the input signal at +2V to +3.5V then the first transistor is turned on and LED #2 should not light.

Maybe the emitter and collector of the transistors are connected backwards, then the emitter-base of transistor #2 has avalanche breakdown like a zener diode and will cause LED #2 to light dimly.

Shorting the LEDs to turn them off wastes a lot of power.

Here's another idea.

It has some hysteresis.

I don't know how well it works in real life but my computer game says it'll work.

hi i've been working hard on this all day . wow electonics really is a balancing act. very difficult.

however, i managed to make audiogurus circuit work when I added the mosfet as suggested. both led's lit very bright and went very dim , woo hoo! : )

but,just like what happened before, i connected it all to another circuit ( the actual trigger circuit ) and there seems to be a conflict, as once i connected it , it would still work however the 2nd led would not glow as bright : / its like i need to isolate the two circuits in some unusual way ( and have 2 grounds?) ? but i am very inexperienced and have no idea if that even makes sense. lol : P . well, i shall keep reading googling and experimenting.

thanks for all your help guys!

p.s jclrd your circuit was fun to make , nice diagram, but i was unable to make it work, i was a few ohms out on some of the resistors, maybe that was it? i shall try again when i buy a wider selection of resistors. thanks allot lclrd : )

hero, i have yet to try your circuit as i have only just seen it, your computer game looks great for making jpegs too i shall try your circuit soon.

thanks again. : )

harps said:

hi i've been working hard on this all day . wow electonics really is a balancing act. very difficult.


p.s jclrd your circuit was fun to make , nice diagram, but i was unable to make it work, i was a few ohms out on some of the resistors, maybe that was it? i shall try again when i buy a wider selection of resistors. thanks allot lclrd : )


thanks again. : )

Click to expand...

I designed it and simulated all on my computer, I'll do an actual prototype build of it and see what needs tweaking.

Hi ,

They both work good.

In the second circuit schematic:
You could always change the 30K resistor for a llower value until it works at the input voltage your using.

I made a voltage divider to test a 2v. input into it and it worked good.
using 2 LED's rated for Vf 2v. I get around 4. 8v. across the string. Using 9v. supply

the first circuit draws around 158mA. @ 9V.
the second draws around 53mA. @9V.

Even if you don't use these circuits they may still be fun to build for experimental purposes, of learning transistor switching circuits.

Also take note of the orientation of the 2 outputs, on the schematics.